The present invention concerns a transfer device for a machine converting plate or sheetlike matter into package, whereby the lowermost sheet is transferred from a sheet batch to the subsequent processing station.
The patent CH-A-440337, and corresponding U.S. Pat. No. 3,510,126, describes a transfer table provided with telescope-type suction cups, suction being achieved owing to the difference of pressure between two chambers of a body of every suction cup, both chambers being connected to a vacuum pump. In line with this arrangement, it has appeared appropriate to have every suction cup connected at the end of the sheet transfer to a source of pressure for quicker separation of the sheet with regard to the suction table, the quicker response to accelerate production. However, because of present production speeds which are likely to soon reach 10,000 sheets per hour, the present means for having each nozzle alternately blow or such, made of fixed valves connected through flexible air suction or pressure ducts to a movable table and actuated by control means themselves kinematically connected to the shift of the suction table, are no longer able to ensure their function on account of their slow response with regard to the time available for the accomplishment of the various control cycles. Besides that, the air contained in the flexible ducts represents a considerable inert mass retarding pressure and suction to a great extent. Moreover, such flexible ducts have a tendency to develop fatigue fissures.
In the patent U.S. Pat. No. 3,202,420 every suction cup of the movable table is connected through flexible ducts to a fixed valve with a rotary distribution flap switching the nozzle to the atmosphere or to suction.
The patent U.S. Pat. No. 3,226,108 describes a suction table provided with several suction holes. The movable table is connected to a lengthwise distributory housing by means of a cylindrical tube fitted to the table frame, and not by a flexible duct, the tube communicating with all suction holes and being able to slide within the corresponding bore of the distributory housing in the course of the sheet transfer. The bore is provided with two apertures longitudinally separated by an appropriate distance and arranged to connect alternately the suction holes to a source or aspiration or to the atmosphere. If this system has the advantage of discarding the drawbacks of the flexible ducts, it has nonetheless the disadvantage of providing only a limited number of possibilities for regulating the alteration of suction or pressure required for the control of the table. The sucking and blowing nozzles are divided up into several assemblies each of which require its own control cycle.